1. Field of the Invention
The invention relates to a magnetic coupling device for charging an electric vehicle which is used for charging an electric vehicle by using electromagnetic induction.
2. Description of the Related Art
Recently, as a charging system for an electric vehicle, a system of the noncontact type which uses electromagnetic induction has been developed. An example of such a system is disclosed in Japanese Patent Unexamined Publication (Kokai) No. HEI6-14470. As shown in FIG. 36, the disclosed system includes a primary coil unit 1 connected to a charging power source, and a secondary coil unit 2 disposed on the body of an electric vehicle. When the vehicle is to be charged, the primary coil unit 1 is inserted into the vehicle body, thereby joining primary and secondary cores 3 and 4 together so as to constitute a magnetic circuit. Under this state, an AC current is supplied to a primary coil 5, so that an electromotive force is generated in a noncontact manner in a secondary coil 6.
However, the above-described structure is of a so-called junction face opposing type and has the following problems. During the process of inserting the primary coil unit 1, the junction faces of the primary and secondary cores 3 and 4 oppose each other and are then made close together. Therefore, a possible very small error of the insertion depth of the primary coil unit 1 directly affects the gap between the cores 3 and 4. The size of a gap in a magnetic circuit has a large effect on a magnetic resistance. Even if the insertion depth is slightly smaller than a preset value, therefore, the properties of the magnetic circuit are largely changed. For example, leakage fluxes are largely increased.
In such a structure, the junction faces of the core 3 of the primary coil unit 1 are exposed, and hence the faces are easily contaminated, so that the gap of the junction in the magnetic circuit is widened. This produces a problem in that it is cumbersome to clean the junction faces.
In the structure of the prior art, since the primary and secondary units which are flat oppose each other, the projected area of each unit in the insertion direction is large. In order to dispose the secondary coil unit, therefore, a region of a large area must be prepared in the outer face of the electric vehicle. This imposes severe restrictions on the design of the structure and appearance of the electric vehicle.
In addition, if a gap is formed in a portion where the primary and secondary cores are joined to each other, the loss is increased and the efficiency is lowered. In the state where the primary coil unit is inserted into the electric vehicle, therefore, it is preferable to join the primary and secondary cores to each other without forming a gap as far as possible.